Winter Moth Identification and Control

Answer: Winter moths, Operophtera brumata, are invasive defoliator insects originally from Europe. They were first discovered around Nova Scotia during the mid-1900s. These pesky intruders emerge during November through December, sometimes even through January, when female moths lay their eggs in clusters on host plants.

In spring, the eggs begin to hatch, releasing tiny green caterpillars commonly referred to as inchworms and loopers. These small caterpillars only reach about one inch in length but can cause serious damage to deciduous trees and shrubs, including oaks, apple, elms and maples, defoliating them by feeding on their buds and foliage. Many of the young caterpillars crawl up the tree trunks, producing silken threads that can carry them in the wind, a dispersal method called “ballooning,” spreading their destruction from plant to plant.

Around June, the caterpillars finish up their feeding and pupate in the soil until fall, when they transform into adult winter moths. Male winter moths are brown and tan in color, with tiny hairs across their wings. They are strongly attracted to light, commonly found flying by porch lights and headlights. Females are different than the males because they are flightless and grey in color. They can usually be found at the base of the host plants, scurrying up the plants while releasing sex pheromone that attracts males, where the moths will mate and lay more eggs.

As adults, the moths do not cause harm to plant-life, however, with that being said, allowing them to lay more eggs will produce the harmful larvae. There are a few measures you can take to try to control the population of winter moths around your home, though none are guaranteed to prevent or eliminate the problem.

First, you want to determine if you have a problem by examining your trees and shrubs for larvae, green to pink eggs, damaged buds and foliage and, in the winter, female winter moths on and/or around the plants. If you don’t have any, or if you do not have many, you can leave your plants alone. The leaves can handle a little damage. If you have a problem or just want to get rid of these unwanted pests, there are different recommended treatments such as Spinosad or Bacillus thuringiensis (Bt) you can use; consult with a tree-care service for assistance and advice. You can also try putting sticky wraps as barriers around the infected plants to trap them. There are different types of parasitic insects, including a species of fly, that are being researched that feed on winter moths.

Winter moths are hazardous insects that can cause damaging effects on trees and shrubs; however with identification, prevention and treatment, we can help protect our much-loved plants from these bothersome little interlopers.